With urbanization happening at high-speed throughout China, the issue of how to restore vitality in a historic conservation district and to re-use these districts according to the demands of the modern city has been paid more and more attention by scholars from different fields. Nowadays, local residents and scholars focus on the problem of how to combine local history and culture, the special characteristics and traditions of an area with modern city life while keeping its historic essence. The historic conservation districts regeneration does not resume itself to total reconstruction. The paper focuses on the questions: what is the Urban Organic Update Theory and how can it provide a theoretical framework to guide the regeneration of historic conservation districts; how to maintain these districts space texture and integrity while updating the function of historic conservation districts and improving the living environment for the local inhabitants. The thesis begins with of the challenges faced by historic conservation districts in a background of high-speed urbanization. It points out that an important challenge nowadays is that many valuable heritages and historic districts are disappearing in the process of a large-scale of transformation of the old city in China. Then it introduces the Urban Organic Update Theory as a theoretical perspective to address the problem of how to conciliate the preservation of historical districts, with the demands of the current modern city, in China. Some primary methods of Urban Organic Update Theory will be discussed, and further applied in the design proposal for Longxi Street area, in the Dafeng metropolitan area, Jiangsu Province, in China. The research analyses the example of Ju'er Hu Tong in the South LuoGu Lane area in Beijing, mainly introduced in Professor Wu Liangyong's book, to argue that the Urban Organic Update Theory is a suitable theory and method for the regeneration of the historic conservation districts where there exists relatively completed urban texture, original space patterns, and traditional feature buildings. By interviewing and visiting the municipal government and local inhabitants, I got the official information and done my design. The Urban Organic Update Theory emphasizes an adaptive method to achieve the goals of improving and upgrading the living environment for the inhabitants, and explores the potential of the local historical and cultural resources at the same time. The theory is a practical method that argues for preserving, rehabilitating, transforming or removing the buildings in accordance with their comprehensive evaluations. It really has a positive meaning to preserve and update the historic conservation districts organically, dividing the existing buildings into different categories, making different levels of the transformations to the constructions. The respect for traditional features and the original space patterns will contribute to improve the environment and living conditions for the inhabitants and enhance the value of the districts for local inhabitants and tourists. However, this paper mainly discusses the regeneration of historic conservation districts from the view of urban morphology. Economic and environmental issues are not discussed here, and issues such as gentrification and other social consequences of urban regeneration are not addressed either.